This application relates to and incorporates herein by reference Japanese Patent Application No. 11-70443 filed on Mar. 16, 1999.
The present invention relates to a vehicular navigation system which navigates vehicle drivers to a destination along a recommended vehicle travel path.
Various vehicular navigation systems are proposed and used to indicate a recommended vehicle travel path to a destination, thereby navigating vehicle drivers to the destination. The recommended travel path is a series of roads (links) and determined by Dijakstra""s algorithm or the like method based on stored road map data. For example, Dijakstra""s algorithm calculates costs of each link between two intersections (nodes) and determines the series of links that results in a minimum total vehicle travel cost to the destination.
It is a general practice to determine the recommended travel path by using data of links such as expressways, national roads, prefectural roads, city or town roads, and the like. Some of the above roads are narrow, for one-way traffic or for only pedestrians, and hence are restricted traffic-type. Those restricted-type roads are not used in the recommended travel path determination process, because the restricted-type road data are in many cases incomplete or unreliable to be used.
The conventional vehicular navigation system is thus capable of determining and indicating the recommended travel path only to a point where sufficient road data are available, or indicating the recommended travel path which takes an unnecessary detour, even if some restricted-type roads are in fact available for vehicle travel.
It is therefore an object of the present invention to provide a vehicular navigation system which ensures determination and indication of a recommended vehicle travel path by using restricted-type road data.
According to the present invention, a vehicular navigation system uses both link information of normal roads and restricted-type roads in determining a recommended travel path to a destination, and a specific guidance indicative of a travel on the restricted-type road when a vehicle travels on the restricted-type road. The restricted-type roads are defined as roads unavailable to vehicle entry, such as one-way traffic roads or narrow roads.
Preferably, the specific guidance is issued upon travel on the restricted-type road in vocal sound or in a mode different from travel on the normal road.